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United States Patent |
5,625,620
|
Fukushima
,   et al.
|
April 29, 1997
|
Optical disc
Abstract
An optical disc has a base formed by resin, and a reflection layer formed
on the base. On the base, servo areas where servo pits P1, P2 for
providing servo information for sample servo system are formed at
predetermined angular positions of respective tracks on the base. Further,
data areas where data pits Pd for providing data information accessed by
the optical disc drive operative on the basis of the servo pits P1, P2 are
formed between the respective servo areas. In addition, in the servo area
and the data area which are adjacent to each other, between servo pit P2
disposed at the position closest to the data area and data pit Pd disposed
at the position closest to the servo area, anchor pit Pan neglected in the
optical disc drive is provided.
Inventors:
|
Fukushima; Yoshihito (Miyagi, JP);
Fujita; Goro (Kanagawa, JP)
|
Assignee:
|
Sony Corporation (Tokyo, JP)
|
Appl. No.:
|
624646 |
Filed:
|
July 1, 1996 |
PCT Filed:
|
August 25, 1995
|
PCT NO:
|
PCT/JP95/01697
|
371 Date:
|
July 1, 1996
|
102(e) Date:
|
July 1, 1996
|
PCT PUB.NO.:
|
WO96/06432 |
PCT PUB. Date:
|
February 29, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
369/275.3 |
Intern'l Class: |
G11B 007/00 |
Field of Search: |
369/275.1-275.4
|
References Cited
U.S. Patent Documents
5436770 | Jul., 1995 | Muto et al. | 360/51.
|
5533003 | Jul., 1996 | Kobayashi | 369/275.
|
Primary Examiner: Hindi; Nabil
Attorney, Agent or Firm: Maioli; Jay H.
Claims
What is claimed is:
1. An optical disc for use with an optical disc drive comprising,
a base formed of resin;
a reflection layer formed on the base;
a plurality of servo areas on the base where a plurality of servo pits for
providing servo information for a sample servo system are formed at
predetermined angular positions in a plurality of respective tracks;
a plurality of data areas where a plurality of data pits for providing data
information accessed by the optical disc drive operative on the basis of
the servo pits are formed between the respective servo areas, and
wherein the servo area and the data area are adjacent to each other and
include a plurality of anchor pits neglected by the optical disc drive
between the servo pit disposed at the position closest to the data area
and the data pit disposed closest to the servo area.
2. The optical disc as set forth in claim 1,
wherein the plurality of servo pits and the plurality of anchor pits are
respectively formed so that they are radially continuous.
3. The optical disc as set forth in claim 2,
wherein the servo pits and the anchor pits are formed from a track of the
linear circumferential end up to a track of the outer circumferential end
of the base.
4. An optical disc system comprising,
a first recordable/reproducible optical disc;
a second reproduction only optical disc,
wherein the first optical disc comprises a base formed of resin and a
reflection layer formed on the base, and formed on the base are a
plurality of servo areas where a plurality of servo pits for providing
servo information for a sample servo system are formed at a predetermined
angle position in a plurality of respective tracks, forming a data train
for providing data information accessed by an optical disc drive of the
optical disc system operative on the basis of the servo pits between the
respective servo areas, and an area of a mirror portion adapted for
clamping a reproduction signal by the optical disc drive formed between
the servo and data areas adjacent to each other, and
wherein the second optical disc comprises a base formed of resin and a
reflection layer formed on the base, and formed on the base are a
plurality of servo areas where a plurality of servo pits for providing
servo information for a sample servo system are formed at predetermined
angular positions in a plurality of respective tracks, and further
comprising a plurality of data areas where a plurality of data pits for
providing data information accessed by an optical disc drive of the
optical disc system operative on the basis of the servo pits are formed
between the respective servo areas, the areas corresponding to the
respective mirror portions of the first optical disc being adapted to
include therein a plurality of anchor pits neglected by the optical disk
drive.
Description
TECHNICAL FIELD
This invention relates to an optical disc in which tracking control, etc.
is carried out by the sample servo system.
BACKGROUND ART
Hitherto, an optical disc for carrying out recording/reproduction of
information by irradiation of laser beams, magneto-optical discs, various
write-once type optical discs which are, digital audio discs so called
compact discs, and optical video discs, etc. have been put into practical
use.
The compact disc and/or the optical video disc among these optical discs
are reproduction only optical discs, are ordinarily of a structure in
which a reflection layer is formed on a transparent base (substrate) where
data pits corresponding to information signals are formed in a recessed
form.
As the transparent base, because cost can beheld down to a lower level
particularly in the case where those bases are mass-produced, disc-shaped
bases obtained by injection-molding resin such as polycarbonate, etc. are
frequently used. Data pits are arranged and formed as a concave recessed
form on tracks set in concentrical form or in spiral form of the
transparent base.
Moreover, the reflection layer is stacked on the surface where data pits
are formed of the transparent base. Aluminum reflection film is generally
used because of its high reflection factor and good thermal conductivity.
In the reproduction only optical disc of such a configuration, a technique
is employed to detect a difference between quantity of reflected light at
the pit portion and that at the portion where no pit exist, i.e., the
mirror portion when laser beams are irradiated from the transparent base
side to reproduce the pit pattern on the tracks on the basis of the
difference. In this case, in order to carry out precise signal
reproduction free from error by such a technique, it is necessary that a
laser beam spot is precisely irradiated onto the track where a pit pattern
to be read out is formed. For this reason, in the optical disc drive,
tracking servo of the optical pick-up is carried out.
As the optical disc system for scanning, by laser beams, tracks formed in a
concentric form or in a spiral form to carry out recording/reproduction of
various data, there are known the optical disc system of the CLV system
for rotationally driving the optical disc at a constant linear velocity
(CLV) to carry out recording/reproduction of data, and the optical disc
system of the CAV system for rotationally driving the optical disc at a
constant angular velocity (CAV) to carry out recording/reproduction of
data.
Further, there are known, in terms of the servo system, optical discs of
the continuous servo system to carry out tracking control, etc. by using
pre-grooves continuously provided along the tracks, and optical discs of
the sample servo system to carry out tracking control, etc. by making use
of servo areas discretely provided on the tracks.
In the case of the optical discs of the sample servo system, respective
tracks are divided into plural data areas, and two servo pits are
respectively formed in the servo areas between the respective adjacent two
data areas.
Respective two servo pits are formed as so called wobble pits by a
geometrical concavity at positions respectively spaced by a 1/4 track
width in a radial direction from a center line of the track by arrangement
in wobble form in such a manner that the scanning line of the laser beam
spot, i.e., the center line of the track is put therebetween before and
after.
Tracking servo of the laser spot is carried out on the basis of servo pits
arranged in a wobble form. Such servo pits are used for tracking servo as
stated above, and are also utilized for generating a clock signal for the
reproducing system. Accordingly, in the sample servo system, shape and/or
position accuracy of the servo pit are very important for satisfactorily
constituting the reproducing system.
Meanwhile, as the transparent base (substrate) of the optical disc,
injection-molded bases are frequently used as described above. Such
injection-molded base is made up, e.g., in a manner as described below.
Namely, a stamper where the inversion pattern of data pits and servo pits
is formed is fixed within a metal mold to carry out mold-clamping to
inject resin such as molten polycarbonate, etc. into the metal mold in
which the stamper is fixed. Then, pressure is applied to the metal mold
while cooling it. After the resin is solidified, the metal mold is opened
to peel (separate) the resin from the stamper. Thus, an injection-molded
base for an optical disc on which the inversion pattern of the stamper has
been transferred is obtained.
In this case, transfer failure (or unsatisfactory transfer) of pits
resulting from thermal contraction of the base is the problem.
Namely, the base comprised of resin has great coefficient of thermal
expansion, so thermal contraction takes place in the cooling process of
the injection molding and the peeling (separation) process from the
stamper. As a result, multi-transfer (multiple transfer) of pits and/or
deformation of pit shape would take place.
For example, as shown in FIG. 1, a base 1 comprised of resin attempts to
undergo thermal contraction in the cooling process. At this time, because
of the effect for preventing the flow of resin by pressure given by the
metal mold or inversion pits 3 formed at a stamper 2 (which will be called
anchor effect hereinafter), the resin is resultantly in the sticking state
without moving on the stamper 2. However, when attempt is made to peel
(separate) the base 1 from the stamper 2, its stress F is released. As a
result, the base 1 contracts. In this instance, pit shape is deformed,
from difference between contraction quantity at the sticking portion of
the base 1 and that at the peeled (separated) portion thereof, at the
boundary between the portion sticking on the stamper 2 and the peeled
(separated) portion as shown in FIG. 2. As a result, transfer failure (or
unsatisfactory transfer) would take place. Such pit deformation is apt to
take place at pits adjacent to the long mirror portion in which the anchor
effect by the inversion pits is difficult to obtain, e.g., at servo pits.
Namely, the anchor effect by the inversion pits is difficult to obtain at
the portion where the mirror portion is continued over a relatively longer
distance such as the portion between the servo pit and the data pit. As a
result, a portion of the base, i.e., resin moves on the stamper 2 by
thermal contraction. Followed by this, the pit shape is deformed and/or
pits are caused to undergo multi-transfer. Image by the AFM (Atomic Force
Microscopy) indicating the state of deformation of pits is shown in FIG.
3. As is clear from FIG. 3, pits would be formed so as to take a
trapezoidal shape.
As described above, because servo pits are used for tracking servo and are
also used as a clock signal for the reproducing system, if their shapes
are not correct, not only deviation in tracking takes place, but also
deviation in the timing for generation of the clock signal takes place,
with the result that bad influence is exerted on the reproducing system.
This invention has been proposed in view of such actual circumstances of
the prior art, and its object is to provide an optical disc and an optical
disc system in which various pits including servo pits can be formed in a
satisfactory form, and tracking servo and/or generation of clock are
precisely carried out.
DISCLOSURE OF THE INVENTION
An optical disc according to this invention comprises a base formed by
resin, and a reflection layer formed on the base, wherein, on the base,
servo areas where servo pits for providing servo information for sample
servo system are formed at predetermined angular positions of the
respective tracks, and data areas where data pits for providing data
information accessed by an optical disc drive operative on the basis of
the servo pits are formed between the respective servo areas, the servo
area and the data area adjacent to each other including an anchor pit or
pits neglected in the optical disc drive between the servo pit disposed at
the position closest to the data area and the data pit disposed closest to
the servo area.
In the optical disc according to this invention, e.g., the plural servo
pits and the plural anchor pits are respectively formed so that they are
radially continuous.
Moreover, in the optical disc according to this invention, e.g., the servo
pits and the anchor pits are formed from the track of the inner
circumferential end up to the track of the outer circumferential end.
Further, this invention is directed to an optical disc system comprising a
first recordable/reproducible optical disc and a second reproduction only
optical disc, wherein the first optical disc comprises a base formed by
resin and a reflection layer formed on the base, and is such that, on the
base, servo areas where servo pits for providing servo information for
sample servo system are formed at predetermined angle positions of the
respective tracks, data areas which can form data train for providing data
information accessed by an optical disc drive operative on the basis of
the servo pits are formed between the respective servo areas, and an area
of mirror portion adapted for clamping a reproduction signal by the
optical disc drive is formed between the servo and data areas adjacent to
each other; and wherein the second optical disc comprises a base formed by
resin and a reflection layer formed on the base, and is such that, on the
base, servo areas where servo pits for providing servo information for
sample servo system are formed at predetermined angular positions of the
respective tracks, data areas where data pits for providing data
information accessed by an optical disc drive operative on the basis of
the servo pits are formed between the respective servo areas, areas
corresponding to the respective mirror portions of the first optical disc
being adapted to include therein an anchor pit or pits neglected in the
optical disc drive.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a model view showing the state of stamper and base in the cooling
process of a conventional injection molding.
FIG. 2 is a model view showing the state of the stamper and the base in the
base peeling process of the injection molding.
FIG. 3 is a model view in which shape of pits deformed in the injection
molding is depicted on the basis of measurement result by AFM.
FIG. 4 is a cross sectional view showing outline of the essential part of
an example of the configuration of an optical disc to which this invention
is applied.
FIG. 5 is a plan view showing tracks set on transparent base of the optical
disc.
FIG. 6 is a model view showing data pit, servo pits and anchor pit formed
on the transparent base of the optical disc.
FIG. 7 is a plan view showing, in a model form, a more practical example of
disc format of the optical disc.
FIG. 8 is a model view in the vicinity of servo area showing arrangement
state of data pits, servo pits and anchor pit in the more practical
example.
FIG. 9 is a model view in the vicinity of servo area of a magneto-optical
disc employing the disc format of the more practical example.
FIG. 10 is a cross sectional view showing outline of the essential part of
the configuration of the principle of injection molder for preparing
transparent base of the optical disc.
FIG. 11 is a model view in which shape of pits where deformation is
suppressed by the anchor effect in the injection molding is depicted on
the basis of measurement result by AFM.
FIG. 12 is a block diagram showing the configuration of an optical disc
reproducing unit for reproducing the optical disc.
FIG. 13 is a timing chart showing sampling timing of servo pit pattern in
the optical disc reproducing unit.
FIG. 14 is a waveform diagram for explaining the relationship between
I.sub.g and I.sub.off.
FIG. 15 is a characteristic diagram showing the relationship between mirror
length and I.sub.g /I.sub.off.
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of this invention will now be described in detail
with reference to the attached drawings. In the embodiment described
below, this invention is applied to a reproduction only optical disc
employing the sample servo system.
In the optical disc of this embodiment, as shown in FIG. 4, a reflection
layer 12 is formed on a disc-shaped transparent base (substrate) 11 made
up by injection-molding resin.
At the surface on the side where the reflection layer 12 is formed of the
transparent base 11, data pits corresponding to information signals and
servo pits for sample servo tracking are formed in a recessed form.
In the optical disc 10, respective tracks are divided into plural data
areas, and two servo pits are respectively formed at servo areas between
the respective adjacent two data areas.
Namely, tracks 13 in concentrical form or in spiral form are set on the
transparent base 11 as shown in FIG. 5, wherein these tracks 13 are
divided into plural data areas ARd, and servo areas ARs are respectively
provided between the respective adjacent two data areas ARd.
Further, data pits are formed in the data areas ARd on the tracks 13. On
the other hand, two servo pits are respectively formed in the servo areas
ARs between the respective adjacent two data areas ARd. The servo area ARs
where servo pits are formed is shown in a model form in FIG. 6.
As shown in the FIG. 6 mentioned above, a mirror portion RFfs extending by
a predetermined distance from the first data pit Pd of the initial end
side of the data area ARd is provided in the servo area ARs, and servo
pits P1, P2 are formed so that distance d in a radial direction from the
center line C becomes equal to 1/4 track width by arrangement in wobble
form such that the center line C of the track is put therebetween before
and after.
Further, in the optical disc 10, pit Pan unnecessary for carrying out data
access is formed between the servo pits P2 and the data pit Pd. In this
example, such an unnecessary pit Pan is assumed to be called an anchor
pit. This anchor pit Pan serves to prevent deformation of pits P2, Pd
produced in the injection-molding of the transparent base 11.
It is to be noted that, in the optical disc 10 of this embodiment,
respective servo areas ARs are disposed at positions obtained by equally
dividing one round (circumference) of track, and servo pits P1, P2 and
anchor pit Pan are radially arranged and formed.
In a more practical sense, as shown in FIG. 7, for example, this optical
disc 10 is such that one round (circumference) of the track is divided
into 1400 segments (segment 0.about.segment 1399), and those segments are
classified into address segments ASEG and data segments DSEG.
On respective tracks of the address segments ASEG, position information in
the radial direction on the disc, i.e., track numbers and position
information in the tangential direction, i.e., segment numbers are
recorded by pits in advance. Namely, pits are formed in advance at the
time of preparation of the optical disc. These address segments ASEG exist
every 14 segments and 100 address segments exist with respect to one round
(circumference) of track. The portion from a certain address segment ASEG
to the next address segment ASEG is one frame, and one round
(circumference) of track consists of 100 frames. 13 segments between
continuous two address segments ASEG serve as data segment DSEG. As the
data segment DSEG, 1300 segments exist with respect to one round
(circumference). Moreover, respective segments are constituted with areas
corresponding to 216 servo clock pulses (hereinafter simply referred to as
clocks depending upon circumstances), and consist of servo area ARs
corresponding to 24 servo clocks and data area ARd corresponding to 192
servo clocks. At the address segment ASEG, the data area ARd consists of
an address area ARda and a laser control area ARdb.
Further, at the servo area ARs, as shown in FIG. 8, for example, three pits
P0, P1, P2 respectively having lengths corresponding to two servo clock
pulses are recorded in advance in the state where the centers therebetween
are spaced by a length corresponding to five servo clock pulses, and a
focus sample area ARfs having a length corresponding to six clock pulses
is provided.
As stated above, by allowing pits P0, P1, P2 of the servo area ARs to
respectively have a length corresponding to two servo clock pulses, the
portion where no pit is formed, i.e., the area of mirror portions is
reduced. Thus, ghost pit, etc. taking place at the time of disc molding
can be difficult to take place. Further, since RF signals are stably
reproduced from pits P1, P2, it becomes possible to stably generate
various servo signals such as tracking servo signal, etc. on the basis of
RF signals reproduced from pits P1, P2. Furthermore, the distances between
centers of respective pits P0, P1, P2 are caused to be spaced by more than
a predetermined distance, thereby permitting data interference between RF
signals reproduced from respective pits P0, P1, P2 to be extremely
reduced. In order to reduce such data interference between the pits, it is
desirable to allow distances between respective pits P0, P1 and distances
between respective pits P1, P2 to be spaced by more than five servo clock
pulses.
The second pit P1 positioned for a 11.about.12 clock time period and the
third pit P2 positioned for 16.about.17 clock time period are respectively
wobble pits placed at positions shifted by .+-.1/4 track width in the
radial direction of the disc from the center of the track to provide
tracking error information by the difference between the amplitude values
of RF signals reproduced from these pits P1, P2. Moreover, as described
later with reference to FIG. 13, phase information of servo clock is given
by the difference between the amplitude values of both shoulder portions
of the RF signals reproduced from these pits P1, P2 to further such phase
information to thereby provide clock phase information which is not
dependent upon the tracking state.
Further, the first pit P0 existing at the beginning of the servo area ARs
is classified, in dependency upon its position, address mark indicating
that corresponding segment is address segment ASEG, first sector mark
indicating that corresponding segment is the leading segment of the
sector, second sector mark indicating that the next segment is the leading
segment of the sector, and segment mark in the case where the positional
relationship of segment does not correspond to any cases described above.
The first pit P0 becomes address mark in the case where it is located for
3.about.4 clock time period, first sector mark in the case where it is
located for 4.about.5 clock time period, and second sector mark in the
case where it is located for 5.about.6 clock time period. It is to be
noted that start positions of respective sectors will be described later
with reference to FIG. 13. Information indicated by the first pit P0 can
be discriminated by examining the position where reproduced RF signal
takes the maximum amplitude value by the difference maximum detection so
called differential detection method as shown in FIG. 3, for example.
Since information indicating address mark or first sector mark and second
sector mark is or are given by the first pit P0 existing at the beginning
of the servo area ARs in a manner stated above, it is unnecessary to
record sector number or track address in units of sector.
Further, in the optical disc 10, anchor pit Pan having the area
corresponding to three data clock pulses is provided at the leading
portion of the data area ARd. By providing such anchor pit Pan in this
way, the area of the mirror portions is reduced. Thus, bad influence
exerted on servo pit at the time of disc molding is lessened.
In addition, pre-write area AR.sub.PR for ensuring compatibility with a
magneto-optical disc shown in FIG. 9 is provided at the leading portion of
the data area ARd. This pre-write area AR.sub.PR is an unnecessary area in
the reproduction only so called ROM disc.
It is a to be noted that while this optical disc 10 is reproduction only so
called ROM disc, this disc format can be applied to recordable optical
discs such as magneto-optical (MO) disc, etc.
Namely, in the recordable optical disc such as magneto-optical (MO) disc,
etc., grooves Gr are provided, as shown in FIG. 9, at the portion
corresponding to the data area ARd without provision of the anchor pit Pan
to thereby reduce the area of the mirror portions to lessen bad influence
in the disc molding on the servo pit. Since the groove Gr is not used for
the tracking control, accuracy such as depth, etc. is not required. In
this example, data area ARd of the data segment DSEG consists of data area
ARd corresponding to 176.about.368 data clock pulses for recording
ordinary data, pre-write area AR.sub.PR corresponding to 12 data clock
pulses, and post-write area AR.sub.P0 corresponding 4 data clock pulses.
The pre-write area AR.sub.PR is provided for ensuring a distance necessary
for pre-heating until the disc takes a stable temperature with respect to
data recording from the time when the drive unit starts irradiation of
laser and for use as a clamp area for suppressing DC fluctuation (change)
resulting from birefringence, etc. of signal at the time of reproduction.
Moreover, the post-write area AR.sub.P0 is provided for eliminating
erasing remainder of data recorded at the overwrite time, and for ensuring
distance sufficient to avoid data interference taking place by the edge of
the groove. Such optical discs are bulk-erased at the time of shipping.
Further, data having the same polarity as that in the bulk erase direction
is recorded with respect to the pre-write area AR.sub.PR, whereby even if
data is not normally recorded into the pre-write area AR.sub.PR by
insufficient pre-heating of the media, value of the data recorded on the
optical disc is not changed. Accordingly, it is possible to reproduce a
stable signal.
In the reproduction only optical disc 10 of this embodiment, the pre-write
area AR.sub.PR corresponding to 12 clock pulses is not required. However,
since the format is caused to be common to the recordable optical disc,
mirror portion corresponding to 19 clock pulses would be formed by the
focus sample area ARfs having a length corresponding to 7 clock pulses and
the pre-write area AR.sub.PR corresponding to 12 clock pulses.
Accordingly, anchor pit Pan having the area corresponding to three clock
pulses is provided at the leading portion of the data area ARd to reduce
the mirror portion, thus to lessen bad influence exerted on the servo pit
at the time of disc molding.
The transparent base 11 of the optical disc 10 of such a structure will be
described in a manner as described below by an injection molder of a
structure as shown in FIG. 10, for example.
Namely, a stamper 21 where inversion pattern of the servo pits P0, P1, P2,
the anchor pit Pan and the data pit Pd described above is formed is
disposed within a disc-shaped cavity 23 formed by a metal mold 22. Then,
molten resin such as polycarbonate, etc. is injected from a resin
injection hole 24 into the cavity 23 of the metal mold 22 molded-clamped
in this state. Then, pressure is applied to the metal mold 22 while
cooling it, whereby shape of the stamper 21 is transferred onto the resin.
After the resin is solidified, the metal mold 22 is opened to peel off the
solidified resin from the stamper 21 by protrusion of an ejector 25. Thus,
transparent base 11 for optical disc is obtained.
In preparing the base 11 for optical disc by the injection-molding, since
the resin has a large coefficient of thermal expansion, it attempts to
undergo thermal contraction when peeling it in the cooling process and
peeling from the stamper 21, movement of the base 1, i.e., the resin
relative to the stamper 21 is suppressed by the anchor effect by the
inversion pits at the portion where a large number of inversion pits are
formed at the stamper 21.
Namely, in the injection-molding of the base 11 having anchor pit Pan at
the mirror portion ARfs between servo pit P2 and data pit Pd, since
stamper 21 in which inversion pattern of anchor pit Pan is formed in
addition to the inversion pattern of data pit Pd and servo pits P0, P1, P2
is used, movement of the resin relative to the stamper 21 by thermal
contraction is suppressed by the inversion pattern of the anchor pit Pan.
Thus, deformation of data pit Pd and/or servo pit P2 existing in the
vicinity thereof is prevented. As a result, various pits including servo
pits P0, P1, P2 are formed in a satisfactory shape like an AFM (Atomic
Force Microscopy) image of FIG. 11.
As an optical disc reproducing apparatus for reproducing the optical disc
10, there are apparatus as disclosed in the Japanese Patent Application
No. 185323/1993 or the Japanese Patent Application No. 30976/1993 that the
applicant of this application has already filed. Outline of the optical
disc reproducing apparatus will now be described with reference to the
block diagram shown in FIG. 12.
This optical disc reproducing unit (apparatus) comprises a spindle motor 31
for rotationally driving the optical disc 10 at a constant angular
velocity, an optical pick-up 32 for scanning the optical disc 1 by laser
beams, a reproduction amplifier 33 for amplifying a reproduction signal
corresponding to the presence or absence of pit from the optical pick-up
33 to form a RF signal to output it, a channel clock forming section 34
for generating a channel clock CK on the basis of the RF signal delivered
from the reproduction amplifier 33, a demodulating section 35 operative on
the basis of the channel clock CK delivered from the channel clock forming
section 34.
The channel clock forming section 34 has a configuration of a so called PLL
(Phase Locked Loop) circuit, and includes, in a more practical sense, an
A/D converter 40 for sampling the RF signal from the reproduction
amplifier 33 by channel clock CK to digitize it to form pit data to output
it, a phase data forming circuit 41 for detecting error of phase of
channel clock CK with respect to servo pit data on the basis of the pit
data from the A/D converter 40 to output phase error detection data, a
pulse detector 44 for forming servo data from the pit data from the A/D
converter 40 to output it, and a servo pattern detector 45 in which servo
pit pattern is stored in advance, the servo pattern detector 45 being
operative to detect data equal to servo pit pattern from the servo data on
the basis of the servo pit pattern.
More particularly, the phase data forming circuit 41 is composed of a data
latch circuit 42 for latching the pit data by a timing pulse from the
timing generator 49, and a phase generator 43 for performing a
predetermined operation on the basis of the pit data latched by the data
latch circuit 42 to detect phase error between the pit data and channel
clock CK.
Moreover, the channel clock forming section 34 includes a counter 46 reset
with the servo pattern detection pulse from the servo pattern detector 45
being a as trigger pulse to count, by a predetermined number, the channel
clock CK to thereby form a first window pulse for detecting servo pit
pattern of the next segment to output it, and a lock/unlock detecting
circuit 47 for detecting at the timing of the first window pulse from the
counter 46 or a second window pulse from the timing generator 49 whether
or not the servo pattern detection pulse is delivered to thereby detect
whether or not lock of the phase between the channel clock CK and the
servo data has been carried out.
Further, the channel clock forming section 34 includes an intra-segment
counter 48 reset by detection data generated in the case where data equal
to the servo pit pattern is detected within a window indicated by the
first window pulse in the lock/unlock detecting circuit 47 to start a
count operation of the channel clock CK, and the timing generator 49
operative so that when count value from the intra-segment counter 48
becomes equal to a predetermined value, it forms the second window pulse
to deliver it to the lock/unlock detecting circuit 47, and to form a latch
pulse in dependency upon the count value and; to deliver it to the data
latch circuit 42.
In addition, the channel clock forming section 34 includes a D/A converter
53 for converting phase error detection data from the phase generator 43
into data in analog form to output it, a phase compensation circuit 54
comprised of, e.g., a low-pass filter which compensates phase of the phase
error detection signal from the D/A converter 53 to output it, and a
voltage controlled oscillator (VCO) for forming channel clock CK of which
frequency is varied on the basis of the phase error detection signal from
the phase compensating circuit 54 to deliver it to the demodulating
circuit 35.
In the optical disc reproducing apparatus, the channel clock forming
section 34 carries out adjustment for matching between phase of the servo
data and phase of the channel clock CK prior to actual reproducing
operation.
Initially, the optical pick-up 32 irradiates weak laser beams for
reproduction onto the optical disc 10 rotationally driven at constant
angular velocity by the spindle motor 31 to detect its return light. Then,
the optical pick-up 32 allows the return light to undergo photoelectric
conversion to thereby reproduce information recorded on the optical disc
10 to deliver a reproduction signal to the reproduction amplifier 33.
The reproduction amplifier 33 amplifies the reproduction signal at a
predetermined gain to deliver it as RF signal to the A/D converter 40 of
the channel clock forming section 34. The A/D converter 40 is supplied
with channel clock CK of free-running frequency from the voltage
controlled oscillator (VCO) 55 in which oscillating frequency is varied in
dependency upon a voltage delivered thereto. The A/D converter 40 samples
the RF signal by the channel clock CK to digitize it to form pit data to
deliver it to the data latch circuit 42 and the pulse detector 44.
The pulse detector 44 determines the differential value of the pit data to
thereby detect pit data which serves as point of inflection from plus to
minus of a waveform of pit data indicated in analog form of the pit data
to form a data train in which value of detected data is caused to be "1"
and values of other pit data are caused to be "0". Then, the pulse
detector 44 delivers servo data consisting of the data train to the servo
pattern detector 45.
In the servo pattern detector 45, servo pit pattern data which is the same
pattern as the servo pit pattern formed on the optical disc 10 is stored
in advance. The servo pattern detector 45 compares the servo pit pattern
data stored in advance and the servo data, whereby when the servo data
becomes in correspondence with the servo pit pattern data, it delivers a
servo pattern detection pulse to the counter 46 and the lock/unlock
detecting circuit 47.
The counter 46 is supplied with channel clock CK from the VOC 55, and is
operative to reset the count value with the servo pattern detection pulse
being the as trigger pulse. Then, the counter 46 newly counts the channel
clock CK from the reset timing.
In this case, if the channel clock CK outputted from the VOC 35 has correct
phase, the reproduction time of one segment, i.e., the time (period) from
the time when the servo pattern detection pulse is delivered to the
lock/unlock detecting circuit 47 up to the time when the servo pattern
detection pulse is subsequently delivered is, e.g., the time of 296
channel clock pulses. From the facts described above, the counter 46
predicts, by the count value thereof, timing at which the Servo pattern
detection pulse is subsequently delivered to the lock/unlock detecting
circuit 47 to form first window pulse when the count value becomes equal
to 296, which is the above predicted timing, thus to deliver it to the
lock/unlock detecting circuit 47.
The lock/unlock detecting circuit 47 is operative so that in the case where
the servo pattern detection pulse is delivered when the first window pulse
is delivered, it delivers detection pulse to the intra-segment counter 48.
The intra-segment counter 48 is supplied with the channel clock CK from the
VOC 55 similarly to the counter 46 to reset the count value thereof with
the detection pulse from the lock/unlock detecting circuit 47 being as
trigger pulse. Then, the intra-segment counter 48 newly counts the channel
clock CK from the reset timing to deliver this count value to the timing
generator 49.
The timing generator 49 forms latch pulses which are respectively caused to
be at a high level at timings of sampling points of both shoulders away in
point of time by one channel clock (pulse) before and after from the
center points of the respective reproduction waveforms with respect to
servo pits P1, P2 on the basis of the count value delivered from the
intro-segment counter 48 to deliver these latch pulses to the data latch
circuit 42.
The data latch circuit 42 latches, as shown in FIG. 13, pit data from the
A/D converter 20 at timings t.sub.a1, t.sub.a2, t.sub.b1, t.sub.b2 of the
latch pulse delivered from the timing generator 49 to thereby latch, from
reproduction waveform of the servo pit pattern, sampling data a1, a2 at
sampling points of both shoulders away in point of time by one channel
clock before and after from the center point of the reproduction waveform
with respect to the servo pit p1 and sampling data b1, b2 at sampling
points of both shoulders away in point of time by one channel clock before
and after from the center points of reproduction waveform with respect to
servo pit P2. Then, data latch circuit 42 delivers respective latch
outputs to the phase generator 43.
The phase generator 43 detects phase error between the channel clock CK and
servo data by the operation expressed below
phase error data=[(a2-a1)+(b2-b1)]/2
from sampling data a1, a2 at sampling points of both shoulders away in
point of time by one channel clock before and after from the center point
of reproduction waveform with respect to the servo pit P1 and sampling
data b1, b2 at sampling points of both shoulders away in point of time by
one channel clock before and after from the center points of reproduction
waveform with respect to servo pit P2 by making use of symmetry in left
and right directions of reproduction waveform of the servo pit pattern to
deliver it as phase error detection data to the D/A converter 53.
Moreover, the timing generator 49 predicts, by the count value from the
intra-segment counter 28, timing at which the servo pattern detection
pulse is to be subsequently delivered to the lock/unlock detecting circuit
47 to deliver second window pulse to the lock/unlock detecting circuit 47,
e.g., when the count value becomes equal to 296, which is the predicted
timing.
The lock/unlock detecting circuit 47 detects whether or not the servo
pattern detection pulse falls within the second window pulse to thereby
discriminate whether or not lock of phase between the channel clock CK and
servo data has been carried out.
It is to be noted that since the servo pit pattern is not a unique pattern,
there are instances where it may be in correspondence with the pattern of
servo data obtained from information recorded at the data portion. For
this reason, if only the counter 46 is provided, since the counter 46 is
reset even in the case where the servo pattern detector 45 erroneously
detects the pattern of servo data as servo pattern, the first window pulse
outputted from the counter 46 would be outputted at an erroneous timing.
Accordingly, it becomes impossible to carry out phase lock of channel
clock CK with respect to the RF signal.
However, in this channel clock forming section 34, there is provided
intra-segment counter 48 reset when the servo pattern detection pulses are
continuously delivered twice within the timing of the initially delivered
first window pulse and the subsequently delivered first window pulse to
detect the servo pattern detection pulse at the timing of the second
window pulse formed when the intra-segment counter 48 takes a
predetermined count value. For this reason, even if the servo pattern is
not the unique pattern, it is possible to precisely carry out detection of
servo pit pattern.
Accordingly, it is possible to deliver the latch pulse at the timing where
the data latch circuit 42 can precisely latch the servo pit pattern.
The D/A converter 53 converts the phase error detection data into data in
analog form to thereby form a phase error detection signal to deliver it
to the VCO 55 through the phase compensating circuit 54.
The VOC 55 varies frequency of the channel clock CK outputted in dependency
upon the phase error detection signal to feed the frequency varied channel
clock CK back to the A/D converter 20, and to deliver it to the counter 46
and the intra-segment counter 48.
The optical disc reproducing unit (apparatus) is placed in a stand-by
(waiting) state when lock of the phase of the channel clock CK with
respect to the RF signal is established.
When reproduction of information is designated (instructed) in the stand-by
state, the optical disc reproducing unit delivers a reproduction signal by
the optical pick-up 32 to the demodulating circuit 35 as RF signal through
the reproduction amplifier 33.
The demodulating circuit 35 is supplied with the phase-locked channel clock
CK from the VOC 35 to demodulate reproduction data from the RF signal on
the basis of the channel clock CK to output the reproduction data through
output terminal 36.
As is clear from the foregoing description, in the optical disc reproducing
apparatus of the sample servo system, since it is possible to grasp
(recognize), at all times, the position on the optical disc that the laser
spot scans after the phase is locked, even if excess anchor pit is
provided, it is possible to reproduce data without any problem.
In order that various pits including the servo pits P1, P2 are formed in a
satisfactory form like AFM image as shown in FIG. 11 mentioned above, the
(time) interval a between the data pit Pd and the anchor pit Pan and the
(time) interval b between the anchor pit Pan and the servo pit P2 are
important. If such (time) interval is too great, sufficient anchor effect
cannot be obtained in the injection molding of the base as in the case of
the prior art, giving rise to deformation of the pit.
In the optical disc reproducing apparatus, with respect to signal level
(current value) of RF signal outputted through the reproduction amplifier
33 from the optical pick-up 32, as shown in FIG. 14, the signal level of
RF signal reproduced from servo pits in the state caused to undergo
off-track by 1/4 track width from the so-called just track state is
assumed to be off track level I.sub.off, the signal level of RF signal
reproduced from servo pits in the just track state is caused to be track
level I.sub.on, and the maximum value of the signal level of RF signal
reproduced multi-transfer pits is assumed to be multi-transfer pit level
I.sub.g. Under such condition, respective samples in which the length of
the mirror section of the servo area is varied without provision of anchor
pit Pan are prepared to measure the off track level I.sub.off, the on
track level I.sub.on and the multi-transfer pit level I.sub.g to determine
the relationship between the length of the mirror portion and I.sub.g
/I.sub.off. Thus, result as shown in FIG. 15 is obtained. In FIG. 15, the
respective black circles .circle-solid. represent measured results of
respective samples.
Namely, between the length of the mirror portion and I.sub.g /I.sub.off
(according as I.sub.g /I.sub.off becomes greater, tracking error is apt to
take place), there exists a correlation as shown in FIG. 15 such that when
the length of the mirror portion is above 13 .mu.m, I.sub.g /I.sub.off is
increased to more of a degree. Thus, it is seen that as the length of the
mirror portion becomes greater, multi-transfer pits are apt to take place
to more of a degree. When the length of the mirror portion is less than 13
.mu.m, multi-transfer hardly takes place. From the facts described above,
it is preferable that the (time) interval between the data pit Pd and
anchor pit Pan and the anchor pit Pan and the servo pit P2 are both set to
less than 13 .mu.m.
As material of such transparent base, there may be employed ordinary resin
used in the injection molded base in the optical disc, e.g., acrylic
resin, polycarbonate resin, polyolefine or epoxy resin, etc.
Moreover, as reflection layer formed on the transparent base, high
reflection factor film ordinarily used in the reproduction only optical
disc, such as, for example, aluminum thin film, etc. may be employed.
Since optical disc of such a configuration is of a structure in which
various pits are formed in a satisfactory form on the transparent base,
the tracking control and/or generation of clock are precisely carried out.
Thus, satisfactory reproduction characteristic can be obtained.
It is to be noted that while the above-described optical disc is of a
structure in which one anchor pit is formed between the data pit and the
servo pit on the transparent base so that mirror portion between the data
pit and the servo pit is not continuous, a plurality of anchor pits may be
formed without being limited to a single anchor pit.
In addition, while explanation has been given in this embodiment by taking
the example of the reproduction only optical disc, this invention is not
limited to such optical disc. If the sample servo system is employed, this
invention may be applied to a rewritable optical disc such as
magneto-optical disc, etc. or write-once type optical disc. Also in this
case, similar effects/advantages are exhibited.
Anchor pit Pan is provided at the mirror portion ARfs between the data pit
Pd and the servo pit P2 as in the case of the optical disc 10 of this
embodiment to thereby reduce the area of the mirror portions ARfs, thus
making it possible to lessen bad influence exerted on the servo pits at
the time of disc molding.
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